Salmonella typhimurium between 2000 and 2012: Antimicrobial resistance and PFGE patterns of isolates from animals, humans and food

Abstract

Salmonella Typhimurium is an important zoonotic pathogen with high levels of antimicrobial resistance. In the present study, we compared the pulsed-field gel electrophoresis (PFGE) and antimicrobial resistance patterns of 275 S. Typhimurium isolates collected between 2000 and 2012: 93 from humans, 111 from animals and 71 from food. A high rate of antimicrobial resistance was detected (71.6%). Multidrug resistance (MDR), defined as phenotypic resistance to three or more antimicrobial classes, was detected in more than half of the isolates (54.9%). The proportion of MDR isolates was the highest in animals (43%), followed by food (30.5%) and humans (26.5%). Among 27 phenotypically determined resistance patterns, three were found to be most common: ACNaSuT (19.3%), ACSuT (12%) and ASuT (11.3%). The first two patterns were the most prevalent in animal isolates (47.2% and 51.5%, respectively), while ASuT isolates were most commonly obtained from humans (58.1%). Macrorestriction with XbaI revealed 72 pulsotypes in nine clusters (A to I) and 19 unique pulsotypes (X1-X19). By far largest cluster F with 29 pulsotypes comprised 58.2% of tested isolates and included 53.8% animal, 26.3% food and 20% human isolates. Two thirds (66.3%) of the isolates in this cluster were MDR. The second largest was cluster E with 11.4% isolates of 12 pulsotypes, including 59.4% human, 31.3% food and 9.4% animal isolates. MDR was detected in 78.1% isolates with the most prevalent resistance pattern ASuT. Cluster I (16 isolates, 2 genotypes) consisted of 87.5% human and 12.5% animal isolates. The majority of these isolates (81.3%) were sensitive to tested antimicrobials and MDR isolates (12.5%) were of ASuT resistance pattern. This work provided valuable data about resistance and PFGE patterns of S. Typhimurium isolates in Slovenia and as global knowledge is essential for improved surveillance of the infections, the data obtained could serve as a base for both national and multistate outbreak investigations.